std::string to const char array

Question

This is the code I am seeking to do

std::string json_str;
const char json[] = json_str;

this is my try

const char json [json_str.size()] = {(char) json_str.c_str ()};

But it gives me the error "cast from 'const char*' to 'char' loses precision"

Please help. Thank you.

C++ doesn't have variable length arrays. An array's dimensions must come from a compile-time constant. — juanchopanza, Aug 14 '15 at 15:54
You can't assign directly to an array from an expression that cannot be reduced at compile time. — πάντα ῥεῖ, Aug 14 '15 at 15:55
Is there a reason you need to `const char*` when you have the string? If you have a function that takes a `const char*` then just use `json_str.c_str()` as the parameter. — NathanOliver, Aug 14 '15 at 15:55
@NathanOliver I suppose you're right; document.Parse (json_str.c_str()) does compile; now to see if it works or not — xinthose, Aug 14 '15 at 15:59

score 2 · Answer 1 · answered Aug 14 '15 at 15:55

2

#include <string>

int main() {
    std::string json_str;
    const char *json = json_str.c_str();
    return 0;
}

answered Aug 14 '15 at 15:55

alifirat

3

This should come with at least a short discussion of the lifetime of the buffer pointed to by `json`. – Angew is no longer proud of SO Aug 14 '15 at 15:57

score 1 · Answer 2 · answered Aug 14 '15 at 16:01

Possible solutions that come to mind:

std::string json_str;
const char* json = json_str.c_str();

You can use json as long as json_str is alive.

std::string json_str;
const char* json = strdup(json_str.c_str());

You can use json even after json_str is not alive but you have to make sure that you deallocate the memory.

2 Answers2